The present invention relates to electromechanical devices and in particular to a relay-like device which is operated by magnetic and manual forces.
To improve efficiency and reliability, it is desirable to operate an electromagnetic switching device with an electromagnetic coil that is driven by a relatively small current. An application thereof might be operation of an automobile accessory such as a defogger, either directly or through a timer. A straight-forward approach known to the prior art is to operate the accessory through a conventional relay that is actuated by a switch (the relay can be self-held through a timer). However, such apparatus requires a substantial current to flow through the switch and relay coil so that the relay armature can be drawn the usual distance. Such relatively high currents require relatively large and inefficient components. For environments such as an automobile where significant vibration is present, it is necessary to have the path travelled by the relay armature sufficiently long to prevent vibrations from causing inadvertent closure of the relay contacts. This practical requirement further increases the power required to drive a relay coil.
In applications where it is necessary to drive a remote accessory for a predetermined time interval, a momentary contact switch can be used to initiate operation of a timer which holds a relay in its closed position for this interval. This known system requires separate installations for the switch and the relay and wiring running therebetween. Having more than one assembly location increases the overall cost of the apparatus as well as the labor cost associated with the installation.
Examples of the prior art are given in U.S. Pat. Nos. 4,095,213 and 3,662,288.